The present invention relates to a seat belt tightening apparatus for rotating a takeup shaft of a retractor in a seatbelt retracting direction at a vehicle collision and a starting device for actuating the seat belt tightening apparatus or an air bag apparatus for protecting a vehicle occupant from an impact at a collision by means of an air bag inflated suddenly by a gas. More particularly, the present invention concerns improvements of an erroneous-actuation preventing mechanism of the starting device.
In recent years, passive restraining apparatuses, such as seat belt tightening apparatuses and air bag apparatuses, have been used extensively for the purpose of protecting vehicle occupants at the time of an emergency such as a vehicle collision or the like.
The aforementioned seat belt tightening apparatus is arranged such that a piston is coupled to one end of a wire member wound around a pulley pivotally attached to a takeup shaft of, for instance, a retractor, and a tensile force is exerted on the wire member by means of a thrust caused by the expansion pressure of gaseous matter acting on the piston which is slidably accommodated in a cylinder. As the wire member retracts and drives the shaft of the retractor in a webbing taking-up direction, a webbing which is applied to the occupant is retracted at the time of an emergency.
In addition, the aforementioned air bag apparatus is arranged as follows. A module which includes a center pad, a folded air bag, an inflator (gas generator), and the like is accommodated in, for instance, a steering wheel. The inflator is ignited at a vehicle collision, and as the air bag is instantly inflated by the suddenly burned gas, the body of the occupant is received by the inflated air bag, thereby reducing the impact applied to the human body to a low level.
As starting devices for actuating the seat belt tightening apparatus and the air bag apparatus by detecting the vehicle collision, a mechanical-type starting device is known which is arranged as follows. A firing pin which is normally held at a nonoperable position is ejected toward a detonator by making use of the operation of an inertial mass which is displaced by an inertial force occurring during a vehicle collision, for example. This causes ignition powder to be ignited, and the seat belt tightening apparatus or the air bag apparatus mentioned above are actuated by an explosive force thereof.
As for assemblies of the seat belt tightening apparatus or the air bag apparatus, which are provided with the mechanical-type starting devices, the starting devices must not be actuated before their installation in the vehicle, and must be provided with an erroneous-actuation preventing mechanism. Accordingly, mechanical-type starting devices provided with various erroneous-actuation preventing mechanisms have been proposed. For example, those disclosed in Japanese Utility Model Unexamined Publication No. 83862/1992, U.S. Pat. No. 5,129,680, and the like are known.
The collision sensor (starting device) disclosed in Japanese Utility Model Unexamined Publication No. 83862/1992 is provided with a safety device which comprises an ignition pin (firing pin) urged toward a detonator, an inertial mass adapted to move on collision, and a rotating member (trigger means) having a lever for urging the inertial mass in a direction opposite to the direction of the collision and adapted to retain the firing pin, the safety device further comprising interfering means for locking or unlocking the inertial mass or the lever. The collision sensor is prevented from being actuated erroneously (being exploded) by locking the movement of the inertial mass by means of the interfering member of the safety device which is set in a locked or unlocked position by the rotation of a rotating shaft.
However, with the starting device in which the firing pin is collides with the detonator which is provided with ignition powder, the inertial mass, the firing pin, and energy supplying means, such as a coil spring, for imparting impact energy for the detonator to the firing pin are formed as separate members. For this reason, even if the movement of the inertial mass is restricted to set the starting device in the nonoperable state, since the firing pin still holds the impact energy for igniting the detonator, there is a possibility of the starting device being actuated as the trigger means is released by some unexpected factor even if the movement of the inertial mass is prevented.
This is attributable to the following, since the inertial mass is disposed in a limited space, it is difficult to increase the energy for moving the trigger means, and the response time of the starting device from the time the inertial mass moves until the ignition powder is ignited must be minimized. For this reason, a retaining allowance at an abutment portion between the firing pin and the trigger means for retaining the firing pin is generally small, so that a setting is provided such that the retention of the firing pin is canceled by the slightest movement of the trigger means. Accordingly, there has been a problem in that the trigger means is released inadvertently if an impact such as a drop is imparted to an assembly provided with such a starting device, or if a deformation or the like is present in the case of the starting device.
Accordingly, acceleration sensors disclosed in U.S. Pat. No. 4,955,638 and the like comprise a safety device (erroneous-actuation preventing mechanism) which has setting members respectively provided with a portion which interferes with the displacement of a sensor mass (inertial mass) supported to be moveable in a direction opposite to the direction of acceleration to be able to undergo displacement by means of an inertial force occurring when an acceleration of a predetermined level or more acts thereon, and a portion which interferes with the displacement of energy releasing means (firing pin) constantly supported resiliently to be capable of undergoing displacement toward an actuating position for releasing the energy. In other words, since the erroneous actuation of the acceleration sensor is prevented by setting the displacement of both the inertial mass and the firing pin in a restricted state by means of the positions of the setting members, it is possible to prevent the firing pin from colliding against the detonator should the retention of the firing pin be canceled in the event of such as the breakage of the trigger means.
In addition, a preloader sensor (starting device) disclosed in U.S. Pat. No. 5,129,680 comprises releasing means for setting the preloader sensor in a nonoperable state and an operable state; urging means for urging the releasing means in a direction in which the preloader sensor is set in the nonoperable state; and joining means for joining a webbing retractor to a vehicle body and having a moving locus at a position in which the joining means interferes with the releasing means. The joining means is adapted to set the releasing means in a state capable of actuating the preloader sensor in a state in which the joining means interferes with the releasing means against the urging force of the urging means by moving a predetermined distance on the moving locus. The joining means is also adapted to set the releasing means in a state preventing the actuation of the preloader sensor by means of the urging force of the urging means in a state in which the joining means does not interfere with the releasing means.
Accordingly, in the webbing retractor before installation in the vehicle, the preloader is prevented from being actuated erroneously (exploded) by virtue of the urging means and the releasing means for setting the preloader sensor in the nonoperable state. Then, if the webbing retractor is joined to the vehicle body by means of a releasing bolt which is the joining means so as to install the webbing retractor in the vehicle, the releasing bolt interferes with the releasing means and sets the releasing means in the state capable of actuating the preloader sensor, thereby rendering the preloader sensor operable simultaneously with installation on the vehicle body.
However, in the case of the erroneous-actuation preventing mechanism for preventing the erroneous actuation of the starting device by preventing the movement of the inertial mass and the firing pin as in U.S. Pat. No. 4,955,638, there is a gap between the setting member for restraining the displacement of the firing pin and a retaining portion of the firing pin, so that the firing pin is movable toward the detonator by the portion of that gap with respect to the setting member. Accordingly, if an unexpected impact acts on an assembly provided with such a starting device, and the retention of the firing pin by the trigger means is canceled, the firing pin moves by the portion of the gap until the retaining portion abuts against the setting member. Then, since the firing pin the retention of which by the trigger means is canceled cannot return to its original position by itself, if the erroneous-actuation preventing mechanism is released, the firing pin which is not retained by the trigger means collides against the detonator and ignites the same. Therefore, such a starting device additionally requires a separate mechanism for pushing back the firing pin to a predetermined position, and the structure becomes complicated, so that there are problems in that the number of components used increases, the assembly efficiency is poor, and the manufacturing cost is high.
Meanwhile, in the case of the preloader sensor disclosed in U.S. Pat. No. 5,129,680, the preloader sensor is set in the operable state by tightening the releasing bolt which is an upper attaching bolt for the webbing retractor. Therefore, if the upper attaching bolt is tightened first at the time of installing the webbing retractor in the vehicle, there is a possibility of the preloader being erroneously actuated during the operation of tightening a lower attaching bolt.
In addition, the releasing bolt, which is the upper attaching bolt, sets the releasing means in the state capable of actuating the preloader sensor as a tip portion of the bolt interferes with the releasing means at the time of tightening, so that a sufficient length of the bolt is required. In the event that a releasing bolt having a different length is used as the upper attaching bolt to be used, or if the tightening of the releasing bolt is not carried out completely, there is a possibility of the preloader sensor being installed in the vehicle body with the preloader sensor remaining in the nonoperable state. In other words, even if the upper attaching bolt is tightened incompletely, it is possible to carry out the subsequent operation of installation on the vehicle body such as the fitting of interior trim for covering the webbing retractor. Hence, there is the possibility of the operation of installation on the vehicle body being finished with the preloader sensor remaining in the nonoperable state.